The present invention relates to improved golf club shafts.
In general, conventional metallic golf club shafts comprise their body portions which are formed in a stepped configuration by cold-drawing a tubular chrome molybdenum steel material of wall thickness equal or even in any portion thereof. The gravitational centers of such conventional golf club shafts are located in a position ranging between 50% and 54% of their overall length from their ends of small diameter in terms of values obtained by dividing by the overall length the distance from such ends to the positions of the gravitational centers.
What is called the swing balance or the swing weight of the golf club is the turning moment around a constant point on the club shaft which is located 355.6 mm (14 inches) inwardly from the grip end of the golf club. In a plurality of golf clubs which are all equal in the values of their turning moments thus identified as the swing balance or the swing weight, one or those in which the positions of the gravitational centers are nearer located to the large-diameter side end, namely, the grip end of the club can be still more increased in their head weight.
However, in the foregoing conventional type golf club shafts, it was difficult from the viewpoints of their construction to locate the positions of their gravitational centers so as to be nearer to their largest-diameter ends. For this reason, in order to allow the positions of the gravitational centers to be located nearer to the shaft ends of large diameter, integrally formed golf club shafts as described and shown in, for example, U.S. Pat. No. 3,871,649 and U.K. Patent Application GB 2227418A were constructed such that their large-diameter side end portions are increased in their wall thickness as compared with their small diameter side end portions.
However, if a tubular material of wall thickness equal or even in any portion thereof is cold-drawn into a golf club shaft, the large-diameter side end portion thereof is inevitably thinner in the wall thickness thereof than the small-diameter side end portion thereof.
Under the circumstances, it becomes necessary to use as a shaft manufacturing material a special tube in which the wall thickness thereof is the greatest in an end portion thereof to be formed into a large-diameter side end portion, and is gradually reduced towards the other end portion thereof. Also, an applicable cold-drawing operation is required to form the special material tube into a golf club shaft in which the wall thickness thereof is greater in the large-diameter side end portion thereof and is small in the small-diameter side end portion thereof than in the conventional golf club shafts. This special manufacturing method causes the manufacturing process to be complicated, thereby increasing the manufacuring cost. This is a disadvantage of the special manufacturing method.
It is therefore a primary object of the present invention to provide for an improved metallic golf club shaft in which the position of the gravitational center is located nearer to the large-diameter end portion than in the conventional golf club shafts by using a simple manufacturing process.
Also, it is a second object of the present invention to provide for an improved golf club shaft in which the weight of the head thereof is increased as compared with the conventional golf club shafts while the swing balance thereof remains identical with that of the conventional golf club shafts.